1. Field of the Invention
The present invention relates to an illumination system. More particularly, the present invention relates to an illumination system that reduces noise in a projector.
2. Description of Related Art
FIG. 1 is a schematic cross-sectional view showing a conventional disposition of a color wheel and a light integration rod. FIG. 2 is a perspective view of a conventional light integration rod. As shown in FIGS. 1 and 2, the light integration rod 110 within the illumination system must be positioned as close to the color wheel 120 as possible to increase the optical effect and quality. However, the color wheel 120 spinning at high speed (for example, up to 10800 RPM) generates considerable noise.
The noise has two major sources. One of the sources is the noise originated by the spinning color wheel 120. This type of noise can be reduced through dynamic balancing or using an air-bearing motor. Another source is the noise caused by the wind shear as the color wheel 120 rotates. More specifically, in a conventional color wheel 120, due to the dimensional tolerance of various filters 122 and the assembling tolerance when the filters 122 are mounted to the motor 124, the light output surface of various filters 122 (the surface adjacent to the light integration rod 110) may not be in the same surface. Hence, a gap G is formed between a portion of the filters 122 and the motor 124. Therefore, as the color wheel 120 rotates, a large cyclic pressure variation occurs in the space between the filter 122 and the light integration rod 110, thereby generating the so-called wind shear. Furthermore, the wind shear may cause some resonance inside the light integration rod 110 and intensify the noise problem.
Furthermore, in a conventional light integration rod 110, a width D1 of a first panel 112a or a second panel 112b is greater than a width D2 of a third panel 114a or a fourth panel 114b. In other words, the distance separating the first panel 112a from the second panel 112b is smaller than the distance separating the third panel 114a from the fourth panel 114b. Thus, the number of light reflections between the first panel 112a and the second panel 112b is greater than the number of light reflections between the third panel 114a and the fourth panel 114b. As a result, a light beam 130 incident on the light integration rod 110 emerges with a lesser degree of uniformity. Ultimately, the image projected from the projector has a poor quality.